A nonvolatile semiconductor memory device such as an EEPROM, an AND type flash memory, an NOR type flash memory, and a NAND type flash memory is widely known. Among them, the NAND type flash memory is advantageous in increasing a memory density since each memory cell shares a source/drain diffusion layer.
Select gate transistors for selecting respective blocks in the memory cell array are provided in memory cell array end portions of the NAND type flash memory. A select gate switch transistor for controlling the gate voltage of the select gate transistors is provided in a peripheral circuit.
The select gate switch transistor of the NAND type flash memory is required to have high driving power in order to charge and discharge a gate of the select gate transistors. At the same time, a high voltage corresponding to an erase voltage is applied to the source/drain regions of the select gate switch transistor during data erasing operation of a memory cell. Therefore, it is also required to ensure high degree of reliability.